Diodes are found in many types of electronic circuits and integrated circuits. Diodes come in all sizes, ranging from small signal semiconductor diodes to large high voltage diodes and power generation diodes.
For example, reference is made to FIG. 1 which shows a circuit indicated generally by reference 10 for charging a capacitor 20. A resistor 42 and a capacitor 44 provide a filtered reference at point 52 for the transistor 40 (on its base). The voltage at point 54 will be 0.7 V less than the input voltage 50 (on average). If a positive transient appears at input 50, the voltage at point 54 won't change because of the filter comprising the resistor 42, the capacitor 44 and the transistor 40. A diode 60 prevents the capacitor 20 from discharging through the emitter-collector junctions of the transistor 40 when the voltage at the input 50 falls down under the voltage stored in the capacitor 20.
For the circuit 10 of FIG. 1, the diode 60 functions as unipolar switch or gate with an ON and an OFF state. In the OFF state, the diode blocks the flow of current, and in the ON state the current flows. In the OFF state, the diode looks like an open circuit. In the ON state the diode looks like a closed or short circuit, however, there is a voltage drop, known as the forward bias voltage, when the diode is turned in ON. The forward bias voltage is typically in the range of 0.7 Volts, for a silicon diode and 0.2 V for a Schottky diode.
Ideally a diode would have no forward voltage drop. Since this is not the case, the forward bias voltage needs to be taken account in most circuit designs, and this presents an additional design constraint or factor. For example, in the context of the circuit 10 of FIG. 1, the forward bias voltage drop of the circuit 10 is a factor together with the temperature coefficients of the junctions of the transistor 40 and the diode 60 for which a typical junction will be in the range of −2.7 mV/C.
Accordingly, it would be advantageous to have a diode equivalent circuit which does not exhibit the forward drop voltage characteristics of conventional diodes.